1. Field of the Invention
The present invention relates to power system stabilization systems and methods employing a rechargeable battery system.
2. Description of the Background Art
In the present invention, xe2x80x9cpower system stabilizationxe2x80x9d refers to reducing disturbance of frequency, voltage, active power, reactive power and phase angle that occurs in first equipment generating power, second equipment consuming power and a power system connecting the first equipment and the second equipment together. In a vicinity of an electric furnace load, an electric railways load and other similar, fluctuating loads, voltage and frequency near these loads fluctuate frequently and widely. To prevent this, the devices like a static var compensator and a static var generator are used in order to reduce voltage fluctuations by compensating reactive power.
In case of solar and wind power whose output power fluctuate according to weather condition, the voltage in vicinity of the generator fluctuates frequently and widely, a static var compensator and a static var generator are used in order to reduce voltage fluctuations by compensating reactive power. To prevent an instantaneous voltage drop, a customer uses a small-capacity, uninterruptible power supply and the like. Furthermore, to maintain stability of a system in phase angle, frequency and voltage, in a power system an operational limit is determined for a power transmission line to secure reliable operation. If an accident occurs exceeding the operating limit, the power generator is disconnected.
Conventionally, energy attributed to regenerative-breaking in electric railways is consumed in the form of thermal energy through resistance. Furthermore, when an electric furnace, a rolling machine and the like cause a load fluctuation, a voltage flicker occurs. As a result, lighting appliance, color TVs and the like cause flicker which degrades power quality.
Furthermore, solar power generation and wind power generation provide an output fluctuating with whether conditions. This is a cause of voltage fluctuations and frequency variations in a power system. Conventionally, a single system is used to compensate only for reactive power to overcome such fluctuations. This method, however, only functions to compensate for voltage fluctuations.
Furthermore, instantaneous voltage drop significantly affects computers and other similar electronic equipment. As such, today, with computers and the like widely used, instantaneous voltage drop damages electronic equipment and causes data loss. As such, in the current state a small-capacity, uninterruptible power supply or the like needs to be installed to prevent such disadvantages.
Furthermore, to maintain the stability of a power system, power flow of a power transmission line is limited to be lower in value than a thermal capacity limit in operating the system. In this method, however, the ability of the power transmission line is not fully utilized. As such, efficient operation cannot be achieved.
When you look at a customer""s equipment, regenerative energy in electric railways is discharged into the atmosphere in the form of thermal energy. As such, additional equipment is required. This requires an additional cost for maintaining and operating the equipment and also goes against energy-saving.
The present invention therefore contemplates a power system stabilization system and method employing a rechargeable battery system capable for example of preventing a customer from significantly fluctuating in load and preventing power generation equipment from providing an output significantly fluctuating with weather conditions, to reliably supply power.
The present invention provides a power system stabilization system employing a rechargeable battery system provided between first equipment generating power and second equipment consuming power. The power system stabilization system includes: a detection circuit detecting a difference between the current state and an active power and a reactive power that should be held by a power system connecting the first equipment and the second equipment together; and a control circuit referring to a result of detection obtained by the detection circuit, to control an active power and a reactive power that are output from the rechargeable battery system.
In the present invention, there is detected in a power system a difference between a predetermined active power and reactive power to be held by the power system and the current state thereof and the resultant difference is referred to to control an active power and a reactive power that are generated from a rechargeable battery system. The rechargeable battery system, rapidly responding to a control command value issued from a power system, can be used to control the power system""s active power and reactive power to have a predetermined value. As such, if a customer significantly fluctuates in load or solar power generation, wind power generation and any other similar power generation equipment provides an output that significantly fluctuates with weather conditions, such fluctuations do not have any significant effect on the power system. Thus, the power system stabilization system can reliably supply power.
Furthermore, active power and reactive power can both be used to compensate for a deviation relative to a reference value serving as a control target, to efficiently prevent voltage fluctuation, instantaneous voltage drop, and oscillation of a power generator. Furthermore, for an area with a load exceeding a surge impedance loading (SIL), voltage can be effectively controlled with active power and it can thus also be controlled for an area that cannot be controlled simply with reactive power. The rechargeable battery system can also be used for load leveling and in the form of a single device can have multiple functions and it can thus also be economically advantageous.
More preferably, the detection circuit includes a first detection circuit detecting an actual reactive power of the power system and a second detection part detecting an actual active power of the power system. The power system can have its actual active power and reactive power detected and referred to to control an active power and a reactive power that are generated from the rechargeable battery system. As such, power can be supplied in stable manner in a vicinity of equipment and customers in effect fluctuating in active power and reactive power, such as solar and wind power generation equipment providing an output significantly fluctuating with weather conditions, customers significantly fluctuating in load, such as electric railways and electric furnaces, and the like.
Still preferably, the detection circuit further includes: a voltage deviation detection circuit detecting a difference between a predetermined voltage to be held by the power system and an actual voltage of the power system; and a frequency deviation detection circuit detecting a difference between a predetermined frequency to be held by the power system and an actual frequency of the power system.
A difference between a predetermined voltage to be held by a power system and an actual voltage thereof and a difference between a predetermined frequency to be held by the power system and an actual frequency thereof, can be detected and referred to to control an active power and a reactive power that are generated from the rechargeable battery system. As such, power can also be supplied in stable manner to a location which, while free of significant variations in active power and reactive power, is close to a relatively unstable power supply, a customer significantly fluctuating in load or the like and it is thus influenced by voltage fluctuation and frequency variation.
Still preferably, the control circuit refers to duration characteristic of overload outputs of the rechargeable battery system to control of an output the rechargeable battery system to make the most use of the ability of the rechargeable battery.
Still preferably, the control circuit refers to a rechargeable battery efficiency characteristic according to a charging and discharging cycle period to control an power output of the rechargeable battery system to make the most use of the ability of the rechargeable battery.
Still preferably, the rechargeable battery system can generate active power and reactive power to effectively prevent an instantaneous voltage drop.
Furthermore, as seen from a customer employing it, a power system stabilization system uses a rechargeable battery system provided between a power system and electric railways equipment to absorb regenerative energy attributed to a regenerative-breaking of a vehicle of the electric railways equipment.
Furthermore, since the rechargeable battery system can absorb reactive energy attributed to reactive-breaking of a vehicle of electric railways equipment, not only can the rechargeable battery system prevent voltage variation but also absorb power generated through regenerative-breaking of voltage and again discharge the power to effectively use energy.
The present invention in still another aspect provides a method of stabilizing a power system via a rechargeable battery system provided between power generation equipment and load, including the steps of: detecting a deviation of each of a power generation frequency, a voltage, an active power and a reactive power of the power generation equipment and a linkage-point phase angle of the power generation equipment; and referring to the deviation to control an active power and a reactive power of the rechargeable battery system to supply the load with a predetermined level of power.
As such, power generation equipment""s power generation frequency, voltage, active power and reactive power deviations and phase angle can be detected and each detected deviation can be referred to to control the rechargeable battery system""s active power and reactive power to supply load with a predetermined level of power so as to prevent a customer from significantly fluctuating in load. As such, if solar power generation equipment, wind power generation equipment and the like fluctuate in output with weather conditions, the power system stabilization method employing the rechargeable battery system can prevent such fluctuation in power generation to reliably supply power.